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Understanding Object-Oriented Programming Concepts: Classes, Inheritance, and Interfaces

This text explores foundational concepts of Object-Oriented Programming (OOP) as outlined by Lemay & Perkins (1996). It covers the concept of objects and classes, including instance variables and methods, class creation, and behaviors such as starting an engine in a Motorcycle class. The material discusses inheritance, subclassing, and the importance of interfaces and packages in Java. With practical examples and code snippets, it aids in grasping essential OOP principles, helping to design classes and hierarchies in programming effectively.

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Understanding Object-Oriented Programming Concepts: Classes, Inheritance, and Interfaces

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  1. Thinking in Objects • Analogies: Legos, PCs • Components • Assemblies • Defined interfaces and abstraction Lemay & Perkins [1996]

  2. Objects and Classes • Class • Instance Lemay & Perkins [1996]

  3. Behavior and Attributes • Instance variables define object attributes • Instance methods are functions that operate on object attributes Lemay & Perkins [1996]

  4. Class Creation (1) class Motorcycle { String make; String color; String engineState; void startEngine() { if (engineState == true) System.out.println(“Already on.”); else { engineState = true; System.out.println(“Now on.”); } } } Lemay & Perkins [1996]

  5. Class Creation (2) void showAtts() { System.out.println(“A “ + color + “ “ + make); if (engineState == true) System.out.println(“Engine on.”); else System.out.println(“Engine off.”); } Lemay & Perkins [1996]

  6. Class Creation (3) public static void main(String args[]) { Motorcycle m = new Motorcycle(); m.make = “Yamaha RZ350”; m.color = “yellow”; m.showAtts(); m.startEngine(); m.showAtts(); m.startEngine(); } Lemay & Perkins [1996]

  7. Inheritance • Subclass • Superclass • Inheritance of instance variables and methods Lemay & Perkins [1996]

  8. Class Hierarchy Design Examples • Vehicles (Lemay) • Computers • Sports • Desserts Lemay & Perkins [1996]

  9. Inheritance • Overriding methods • Multiple inheritance prohibited Lemay & Perkins [1996]

  10. Interfaces and Packages • Interface: a collection of methods without definitions, used to indicate special additional methods beyond those inherited by a class from its parent(s) • Packages: a collection of classes and related interfaces • java.lang • Package and class names (e.g., java.awt.Color) Lemay & Perkins [1996]

  11. Subclasses and Subclassing (1) import java.awt.Graphics; import java.awt.Font; import java.awt.Color; public class HelloAgainApplet extends java.applet.Applet { Font f = new Font(“TimesRoman”, Font.BOLD, 36); public void paint(Graphics g) { g.setFont(f); g.setColor(Color.red); g.drawString(“Hi!”, 5, 50); } } Lemay & Perkins [1996]

  12. Subclasses and Subclassing (2) <HTML> <HEAD> <TITLE>Another Applet </TITLE> </HEAD> <BODY> <P>My second Java applet says: <APPLET CODE=“HelloAgainApplet.class” WIDTH=200 HEIGHT=50> </APPLET> </BODY> </HTML> Lemay & Perkins [1996]

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